As described earlier, UDP is a connectionless protocol. This feature allows you to configure the following two types of communications with a NameServer:
Host request — The client or Unified Broker sends a message directly to a NameServer residing on a specific host and listening on a specific port. The IP address represents the actual network location of a specific host. Only the NameServer on the specified host and listening on the specified port receives the message.
Broadcast request — The client or Unified Broker sends a message specifying the UDP broadcast address of the NameServer host and the UDP port number on which the NameServer is listening. The UDP broadcast address represents the entire subnet where a host is located, and you can determine this address using the appropriate operating system commands from any host on the subnet. When a client or Unified Broker sends a UDP broadcast request, every NameServer on any host in the subnet that is listening on the specified port receives the message.
UDP broadcasting insulates the client and Unified Broker from having to know the exact host location of the NameServer. If there is some reason that you need to move the NameServer to a different machine in the same subnet, you can safely do it without having to change your client application or your Unified Broker configuration.
The following figure shows a client and Unified Broker using UDP broadcasting to communicate with the NameServer. Using the UDP broadcast address, 172.20.255.255, this client and Unified Broker can communicate with a NameServer running on any host in the 172.20 subnet.
Thus, you can use UDP broadcasting to support location transparency for a single NameServer. However, as the following figure implies, you can also use UDP broadcasting as the basis to support fault-tolerant NameServers using NameServer replication.
Host request — The client or Unified Broker sends a message directly to a NameServer residing on a specific host and listening on a specific port. The IP address represents the actual network location of a specific host. Only the NameServer on the specified host and listening on the specified port receives the message.
